The present invention is related to a method and apparatus for performing image compression. In particular, the invention eliminates the need for interpolation routines to define image blocks when performing image compression of a source image composed of highly sampled image components and less frequently sampled image components. The invention also reduces the number of image blocks required to perform image compression.
A common method of producing color image information in solid-state imaging systems is to provide a color filter array (CFA) over an image pixel plane of a solid-state imager. Generally, the CFA is configured to produce highly sampled image components (high frequency components) for luminance information and less frequently sampled image components (low frequency components) for color information. For example, the CFA may have a repeated pattern of several rows of green pixels followed by a single row of alternating red and blue pixels. In such a case, the higher frequency green pixels are used to provide luminance information while the lower frequency red/blue pixels are used to provide for color information. An example of such a CFA is illustrated in U.S. Pat. No. 4,876,590 issued to Parulski on Oct. 24, 1989.
The patterning of the CFA can cause difficulties when applying data compression techniques that utilizea discrete cosine transform to compress the image information generated in the above-described solid- state imaging systems. In order to perform data compression, the image information must be divided into a number of image blocks in which spatial samples in the image blocks are equally spaced, i.e., the total image information must be divided into a plurality of image blocks of equally spaced green pixels. The definition of the image blocks is typically accomplished by grouping adjacent green pixels. Interpolation routines must be performed, however, to replace the rows of lower frequency red/blue pixels with interpolated rows of green pixels prior to defining the image blocks and performing data compression, in order to maintain proper spacing between the green pixels.
The requirement for performing the interpolation routines adds complexity and expense to a data compression system. In addition, the speed at which data compression can be performed is reduced by the requirement for interpolating pixel data. Accordingly, it would be desirable to provide a method and apparatus for performing image compression that does not require the higher frequency image components to be interpolated prior to performing a data compression operation.